1. Field of the Invention
The present invention relates to a dielectric block plating process for forming a plated layer by an electrolytic plating process over the surface of a dielectric block having through holes extending from the bottom surface to the top surface thereof.
2. Description of the Prior Art
Generally, a dielectric block plating process for forming a conductive layer comprises the following steps.
(1) washing and roughening the surface of a dielectric block made of ceramic material comprised of TiO.sub.2 and BaO,
(2) coating the surface of the dielectric block with an ground conductive layer through an electroless plating process,
(3) coating a predetermined portion not to be coated with an upper conductive layer of the surface of the dielectric block with a resist material,
(4) coating the surface of the dielectric block with an upper conductive layer by an electroplating process, and
(5) removing the resist material and the ground conductive layer coated with the resist material.
When the dielectric block is plated by the foregoing dielectric block plating process to manufacture a dielectric filter having inner conductors in the through holes and an outer conductor at the surface of the block, the electrolytic solution is liable to stagnate in the through holes of the dielectric block and hence, the surfaces of the through holes may be coated with inner conductive layers having an insufficient thickness. The electric characteristics of such dielectric filter containing inner conductive layers (inner conductors) having an insufficient thickness, do not meet desired electric characteristics.
There is a dielectric block plating process invented to solve the foregoing problem in Japanese Patent Laid-Open Publication No. 59-185795. This conventional dielectric block plating process requires a plurality of electrolytic solution injecting means to be disposed respectively adjacent and opposite to the through holes of a dielectric block. Accordingly, this dielectric block plating process requires the dielectric block to be set exactly at a predetermined position adjacent to the electrolytic solution injecting means.
Another conventional dielectric block plating process employs auxiliary anodes, which are respectively inserted in the through holes of a dielectric block to form inner conductors having a sufficient thickness.